In a wireless communication system having a plurality of base station devices, if communication areas (cells) formed by the plurality of base station devices overlap each other, a signal transmitted from a certain base station device may reach a terminal device existing in a cell of another base station device located near the certain base station device, and the signal may become an interference signal for the terminal device.
It is well known that such interference can be suppressed by beam forming. That is, a base station device performs beam forming such that a beam is directed to a terminal device existing in its own cell (hereinafter, referred to as “own terminal device”) while a null beam is directed to a terminal device existing in a cell of another base station device (hereinafter, referred to as “another terminal device”). Thereby, a signal (interference signal) transmitted from the base station device becomes less likely to arrive at the another terminal device, and thus interference is suppressed (refer to Non-Patent Literature 1 for beam forming).